Method and system for updating software with smaller patch files

ABSTRACT

Rather than comparing an old file with a new file to generate a set of patching instructions, and then compressing the patching instructions to generate a compact patch file for transmission to a user, a patch file is generated in a single operation. A compressor is pre-initialized in accordance with the old version of the file (e.g. in an LZ77 compressor, the history window is pre-loaded with the file). The pre-initialized compressor then compresses the old file, producing a patch file from which the new file can be generated. At the user&#39;s computer, a parallel process is performed, with the user&#39;s copy of the old file being used to pre-initialize a decompressor to which the patch file is then input. The output of the decompressor is the new file. The patch files generated and used in these processes are of significantly reduced size when compared to the prior art. Variations between copies of the old file as installed on different computers are also addressed, so that a single patch file can be applied irrespective of such variations. By so doing, the need for a multi-version patch file to handle such installation differences is eliminated, further reducing the size of the patch file when compared with prior art techniques. Such variations are addressed by “normalizing” the old file prior to application of the patch file. A temporary copy of the old file is typically made, and locations within the file at which the data may be unpredictable due to idiosyncrasies of the file&#39;s installation are changed to known or predictable values.

This application is a divisional of U.S. patent application Ser. No.09/093,591, filed Jun. 8, 1998, now pending.

FIELD OF THE INVENTION

The present invention relates to the updating of computer software byuse of patch files, the generation of such patch files, and thenormalization of files to which such patches are applied.

BACKGROUND AND SUMMARY OF THE INVENTION

Popular computer programs, including computer operating system software,are subject to near-constant revision. Their evolution is sometimes sorapid that, a month after installation, a newer version is available.The newer version may feature additional capabilities, bug fixes, andenhanced compatability with other programs. Accordingly, many usersdesire to update their programs each time a newer version is released.

A user wishing to update a computer program can either acquire a newcopy of the program, or “patch” the old. Patching is growing inpopularity, particularly with the growth of the internet. Patches forupdating many popular computer programs are now commonly available fromsoftware vendor's web sites, allowing users to update their softwareprograms without leaving home.

Patching is an old technology, going back decades. Generally, patchfiles include a series of instructions specifying how a new version of afile can be assembled from snippets of data from an old version of thefile, together with insertions of new data. An exemplary series ofpatching instructions may look like the following:

1. Load old file ABC.EXE into memory;

2. Check that the file data at offset 16 reads “Version 2.04”; if not,fail;

3. Copy bytes 1 through 16 of the old file into a new file;

4. Next, insert the ASCII text “Version 3.02” into the new file;

5. Next, copy bytes 22-256 of the old file into the new file;

6. Next, insert the following hex data into the new file:

09 03 00 01 60 6B F5 D5 3B 59 1A 10 B5 69 08 00

7. Next, copy bytes 289-496 of the old file into the new file;

8. Next, copy bytes 505-512 into the new file;

9. Close the new file and store under name ABC.EXE.

It will be recognized that the foregoing instructions result in an newversion of file ABC.EXE in which:

the first 16 bytes are unchanged;

the version number stored at bytes 17-28 has been rewritten from“Version 2.04” to “Version 3.02”

bytes 22-256 are unchanged;

32 bytes of hex data at bytes 257-288 have been rewritten;

bytes 289-496 are unchanged;

bytes 497-504 have been omitted; and

bytes 505-512 have been shifted to immediately follow byte 496.

Due to the replication of long strings of data from the old file in thenew file, the series of patching instructions is much shorter than thefile being patched. This size economy is the reason patching is morepopular than transferring an entire copy of the new file.

The process of generating patching instructions, like those reproducedabove, is typically automated. The vendor inputs copies of the new andold program file to a pattern matching algorithm, which tries to locatewhere strings of data in the new file can be found in the old file.Where such matches are found, appropriate copy instructions aregenerated and added to the collection of instructions that will form thepatch file. Where data in the new file has no counterpart in the old,the new data is literally specified in the patch file. When completed,the patch file—in conjunction with the old version of the file—containsall the information necessary to generate the new version of the file.

After the patching instructions have been specified in a patch file, thefile is typically compressed to minimize its size and download time(assuming an internet or other network download). Many suitablecompression processes are known. Various implementations of the popularLZ compression algorithms typically reduce file sizes on the order of50%.

After the patch file is compressed, it is transferred from the vendor'scomputer to the user's computer—by internet in this example. On theuser's computer a decompression process is first performed to restorethe patching instructions to their original form. Then the variousoperations specified by the patching instructions are performed,transforming a copy of the user's old file into the latest version.

While the just-described process is a great improvement overtransferring a new copy of the complete program file from the vendor tothe user, it still suffers from certain drawbacks.

One is the size of the compressed patch file. As discussed below, patchfile sizes considerably smaller than those resulting from prior artprocesses are possible, reducing internet download times (or reducingneeded disk storage) commensurately.

Another problem is that the version of the old file on the user'scomputer may not precisely match the version distributed by the vendor.In particular, the file may have been tailored in certain respects—atthe time of installation on the user's computer—to better conform toparticular characteristics of the user's computer. Thus, for example, aprogram file as installed on a single-processor computer may be slightlydifferent than the “same” program file as installed on a multi-processorcomputer. Unless the precise contents of the file as installed on theuser's computer are known, patching is a risky business.

When a software vendor knows that there are several different versionsof a file to be updated, the vendor may publish a multi-version patchfile. Such a patch file can be a concatenation of several different setsof patching instructions, each one applicable to a different version ofthe file. The drawback of this approach is that half, or more, of thepatch file is superfluous data—inapplicable to the file stored on aparticular user's computer. Thus, its download time is far longer thanis really necessary.

Another type of multi-version patch file has a general set of patchinginstructions (for code that is consistent through all versions of theold file), together one or more specialized sets of patchinginstructions (for code that is different between different versions ofthe old file). Branch instructions in the patching file examineparticular characteristics of the old file, and apply the appropriateset of specialized patching instructions.

Again, this approach suffers by reason of more patching data than isneeded for any given user.

In accordance with a preferred embodiment of the present invention, theforegoing and additional drawbacks of the prior art are overcome. Thetwo distinct operations of pattern matching and compression (performedon the vendor's computer in prior art patch generation techniques) arereplaced by a single operation that both compares old and new fileversions, and produces a compressed output by which the latter can begenerated from the former. Likewise, the two distinct operations ofdecompression and patch instruction application (performed on the user'scomputer in the prior art) are replaced by a single operation that bothdecompresses the patch file data and results in recreation of the newfile. The patch file generated and used in these processes is ofconsiderably reduced size—sometimes half the size of compressed patchfiles produced by prior art approaches.

In the preferred embodiment, these advantages are achieved by use ofcompression/decompression processes in which the compressor (anddecompressor) is pre-initialized in accordance with the old version ofthe file being updated. In implementations using LZ77-type compression,this pre-initialization takes the form of preloading the respectivecompressor/decompressor history windows with the old version of thefile. On the vendor side, the new file is the applied to thepre-initialized compressor, yielding the patch file as output. Thecompressor both identifies redundancies between the new file and the oldfile (with which the compressor's history window has been preloaded),and provides a highly compressed output. On the user's side, the patchfile is decompressed using a parallel process.

(LZ77 is a form of adaptive dictionary compression named afterLempel/Ziv's 1977 paper “A Universal Algorithm for Sequential DataCompression,” IEEE Trans. Info. Theory, IT-23 (3), pp. 337-343. Manyvariants of this technology are known, including LZR (Rodeh's 1981implementation), LZSS (Bell's 1986 implementation), LZB (Bell's 1987implementation), LZH (Brent's 1987 implementation), etc. Further detailscan be found in the book Text Compression by Timothy Bell et al,Prentice Hall, 1990, and in Microsoft's U.S. Pat. Nos. 5,572,206,5,521,597, and 5,455,577. A searching technique for identifying matcheswithin the history window is disclosed in pending application Ser. No.08/783,491, filed Jan. 14, 1997. The disclosures of these patents andpatent application are incorporated by reference.)

The same technique is similarly applicable to non-LZ77 compressors. Forexample, in LZ78-type compressors, pre-initialization can beaccomplished by first applying the old file to the compressor, therebycausing the compressor to build a string dictionary comprising excerptsof the old file. The new file is thereafter applied to the samecompressor. The pre-initialization of the compressor's string dictionaryallows it immediately to effect high compression efficiencies due tomatches between the new file and the pre-initialized string dictionary.

(LZ78 is another form of adaptive dictionary data compression, this onenamed after Lempel/Ziv's 1978 paper, “Compression of IndividualSequences Via Variable-Rate Coding,” IEEE Trans. Info. Theory, IT-23(5), pp. 530-536. Many variants of this, too, are known, including LZW(Welch's variation), LZFG (Fiala and Green's variation), and UNIXCompress.)

In LZ78-type systems, the pre-initialization of the decompressor isslightly more complex than in LZ77-type systems. Rather than copying theold file directly into a history window, a string table must be formed,duplicating the string table in the compressor after pre-initialization(i.e. when the new file was applied). In the preferred embodiment, theuser's computer is provided with both a decompressor and a compressor.The compressor is used to process the old file (from the user'scomputer)—just as was done at the vendor's computer—thereby producing astring table. This string table is then used in the decompressor(effecting its “pre-initialization”) for decompression of the patch filefrom the vendor.

The same pre-initialization approach can be applied to Markov modelcompressors. Again, the old file is first applied to the compressor. Thecompressor generates probability data statistically modeling the olddata file (e.g. calculating the probability of encountering a symbol Xafter seeing a certain number of previous symbols). When the new file isthereafter applied to the pre-initialized compressor, the existingprobability data allows immediate compression efficiencies, producing amuch more compact output file. This file is transferred to the user'scomputer. Again, as with LZ78, the user's computer has a compressor aswell as a decompressor. Again, the copy of the old file on the user'scomputer is applied to the compressor, thereby generating theprobability data with which the decompressor is pre-initialized. Thecompressed file from the vendor is then applied to the pre-initializeddecompressor, regenerating the complete new file on the user's computer.

The preferred embodiment also addresses variant installations of the oldfile on different computers, so that a single patch file can be appliedirrespective of such variations. By so doing, the need for amulti-version patch file is eliminated, further reducing the size of thepatch file when compared with prior art techniques.

In the illustrated embodiment, such file variations are “normalized”prior to application of the patch file. A temporary copy of the old fileis desirably made, and locations within the file at which the data maybe unpredictable due to idiosyncrasies of the file's installation arechanged to predictable values. So doing assures that the data to whichthe patch file is applied will be essentially uniform across allcomputers.

Additional features and advantages of the present invention will be morereadily apparent from the following detailed description, which proceedswith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary computer system used in oneembodiment of the present invention:

FIG. 2 is a block diagram showing a vendor's computer, a user'scomputer, and partial hard disk contents of each.

FIG. 3 shows how the vendor's computer of FIG. 2 can be used to generatea patch file, and the user's computer of FIG. 2 can generate an updatedfile from the patch file, in accordance with one embodiment of thepresent invention.

FIGS. 4A and 4B show one way history windows can be managed during thecompression and decompression processes shown in FIG. 3.

FIGS. 5A and 5B show another way history windows can be managed duringthe compression and decompression processes shown in FIG. 3.

FIG. 6 shows specific series of operations that can be used to normalizea file prior to patching.

FIG. 7 shows how normalization can be used in the generation, andapplication, of patch files.

DETAILED DESCRIPTION

To illustrate the principles of the invention, the following discussiondetails an exemplary embodiment employing LZ77-typecompression/decompression processes. However, as noted above, theinvention is not so limited, but can be applied e.g. to any compressiontechnology in which the compressor adapts to the data to improvecompression efficiency.

FIG. 1 and the following discussion provide a brief, general descriptionof computers used in an exemplary embodiment. While the embodiment isdescribed in the context of computer-executable instructions of computerprograms that run on personal computers, those skilled in the art willrecognize that the invention also can be implemented in combination withother program modules. Generally, program modules include routines,programs, components, data structures, etc. that perform particulartasks or implement particular abstract data types. Moreover, thoseskilled in the art will appreciate that the invention can be practicedwith other computer configurations, including hand-held devices,multiprocessor systems, microprocessor-based or programmable consumerelectronics, minicomputers, mainframe computers, and the like.

With reference to FIG. 1, the computers 20 used in the illustratedembodiment include a processing unit 21, a system memory 22, and asystem bus 23 that couples various system components including thesystem memory to the processing unit 21. The processing unit can be anyof various commercially available processors, including Intel x86,Pentium and compatible microprocessors from Intel and others, includingCyrix, AMD and Nexgen; Alpha from Digital; MIPS from MIPS Technology,NEC, IDT, Siemens, and others; and the PowerPC from IBM and Motorola.Dual microprocessors and other multi-processor architectures also can beused as the processing unit 21.

The system bus can be any of several types of bus structure including amemory bus or memory controller, a peripheral bus, and a local bus usingany of a variety of conventional bus architectures such as PCI, VESA,Microchannel, ISA and EISA, to name a few. The system memory includesread only memory (ROM) 24 and random access memory (RAM) 25. A basicinput/output system (BIOS), containing the basic routines that help totransfer information between elements within the personal computer 20,such as during start-up, is stored in ROM 24.

Computer 20 further includes a hard disk drive 27, a magnetic disk drive28, e.g., to read from or write to a removable disk 29, and an opticaldisk drive 30, e.g., for reading a CD-ROM disk 31 or to read from orwrite to other optical media. The hard disk drive 27, magnetic diskdrive 28, and optical disk drive 30 are connected to the system bus 23by a hard disk drive interface 32, a magnetic disk drive interface 33,and an optical drive interface 34, respectively. The drives and theirassociated computer-readable media provide nonvolatile storage of data,data structures, computer-executable instructions, etc. for the personalcomputer 20. Although the description of computer-readable media aboverefers to a hard disk, a removable magnetic disk and a CD, it should beappreciated by those skilled in the art that other types of media whichare readable by a computer, such as magnetic cassettes, flash memorycards, digital video disks, Bernoulli cartridges, and the like, can alsobe used in the exemplary operating environment.

A number of program modules can be stored in the drives and RAM 25,including an operating system 35, one or more application programs 36,other program modules 37, and program data 38.

Illustrated computer 20 operates in a networked environment usinglogical connections to one or more remote computers, such as a remotecomputer 20B. Remote computer 20B typically includes many or all of theelements described relative to the personal computer 20A, although onlya memory storage device 50 has been illustrated in FIG. 1. The logicalconnections depicted in FIG. 1 include a local area network (LAN) 51 anda wide area network (WAN) 52. Such networking environments arecommonplace in offices, enterprise-wide computer networks, intranets andthe Internet.

When used in a LAN networking environment, the personal computer 20 isconnected to the local network 51 through a network interface or adapter53. When used in a WAN networking environment, the personal computer 20typically includes a modem 54 or other means for establishingcommunications over the wide area network 52, such as the Internet. Themodem 54, which can be internal or external, is connected to the systembus 23 via the serial port interface 46. In a networked environment,program modules depicted relative to the personal computer 20, orportions thereof, can be stored in the remote memory storage device. Itwill be appreciated that the network connections shown are exemplary andother means of establishing a communications link between the computerscan be used.

In accordance with the practices of persons skilled in the art ofcomputer programming, the present invention is described below withreference to acts and symbolic representations of operations that areperformed by personal computers 20, unless indicated otherwise. Suchacts and operations are sometimes referred to as beingcomputer-executed. It will be appreciated that the acts and symbolicallyrepresented operations include the manipulation by the processing unit21 of electrical signals representing data bits which causes a resultingtransformation or reduction of the electrical signal representation, andthe maintenance of data bits at memory locations in the memory system(including the system memory 22, hard drive 27, floppy disks 29, andCD-ROM 31) to thereby reconfigure or otherwise alter the computersystem's operation, as well as other processing of signals. The memorylocations where data bits are maintained are physical locations thathave particular electrical, magnetic, or optical propertiescorresponding to the data bits.

Turning now to FIG. 2, two computers 20A and 20B are shown. Computer 20Ais a user's computer. Computer 20B is a software vendor's computer,remote from the user computer. The aim is to produce a patch file on thevendor computer 20B, and transfer it to the user's computer 20A (bydiskette, by the internet, etc.) so that an updated file can be producedon the user's computer.

User computer 20A includes a hard disk 27 on which a variety of softwarefiles are stored. These include operating system files, applicationfiles, and data. Consider particularly an he application program thatincludes several application files, some of which are executable(binary) files. An exemplary executable file may be ABC.EXE.

File ABC.EXE was obtained, sometime earlier, from the softwarevendor—either on an installation diskette/CD-ROM, or distributed via theinternet. It was—at the time of its installation—the most up-to-dateversion of the file available. A text string indicating the version(e.g. version 2.04) is typically encoded somewhere within the binaryfile.

When file ABC.EXE was originally installed onto hard disk 27 from theinstallation disk, some changes may have been made to the file, asdiscussed below. For the moment, however, assume the file as installedon the hard drive 27 is identical to the file distributed by thesoftware vendor.

Over time, the software vendor has further developed the applicationprogram. Successive versions of file ABC.EXE have been written. Newpurchasers of the program receive from the software vendor the latestversion of the file (e.g. version 3.02). However, the user of computer20A still has version 2.04. The vendor wishes to provide a patch programthat will generate, on the user's computer 20A, the latest version offile ABC.EXE.

The software vendor, naturally, has copies of all prior versions of theapplication program on its computer 20B. Turning to FIG. 3, to generatea patch file to upgrade version 2.04 of file ABC.EXE to version 3.02,the vendor compresses version 3.02 of file ABC.EXE using an LZ77-typecompressor 50 (implemented by suitable programming instructions forcomputer 20B). However, rather than beginning with an empty compressiondictionary 52 (sometimes termed a “history window” or “history buffer”and typically implemented in RAM in computer 20B), the instructionsfirst preload the dictionary with version 2.04 of the file. Thecompression process proceeds, identifying successive “matches” betweenversions 3.02 and 2.04 of the file, and encoding same in the compressedoutput data as “tokens” specifying a particular location in the historywindow where a match was found, and the length (in bytes, bits, etc.) ofthe match. Portions of file 3.02 that do not match either any part ofversion 2.04, or any part of version 3.02 that has already beenprocessed and now is in the dictionary, are encoded in the compressedoutput data stream as literal characters. The programming then causesthe CPU to store the compressed output data from the compression processin a patch file 54. (The patch file may, but Is need not, include otherdata, such as self-extraction instructions, etc.) Due to the substantialredundancy between versions 2.04 and 3.02, the patch file is quitesmall, essentially comprising just the differences between the twofiles.

Patch file 54 is transferred to the user's computer 20A, by means 58such as a diskette, CD-ROM, internet, etc., and is typically stored onthe user's hard disk 27. A parallel decompression process is thenperformed on the user's computer. A history window 56, implemented inRAM of computer 20A, is preloaded with version 2.04 of file ABC.EXE asearlier stored on the user's hard disk 27. The compressed data in patchfile 54 is then applied to a decompressor 58 (again implemented byappropriate programming of the CPU of computer 20A). Decompressionproceeds in accordance with the token and literal information encoded inthe compressed data, copying excerpts from the history window 56, andinserting literal characters as appropriate, to regenerate version 3.02of file ABC.EXE on the user's computer 20A. The regenerated file is thenstored on the user's hard disk 27 (not shown).

The history window in the illustrated embodiment is large, such as 8 or16 megabytes, although smaller sizes can alternatively be used. A largehistory window usually allows the whole of the older version of fileABC.EXE to be loaded therein. As the newer version of the file isprocessed during compression (or as the patch file is processed duringdecompression), the new data can be added to the history window. If thewindow becomes full, the older version can slide out as it is displacedby data from the newly processed file.

This arrangement is shown in FIGS. 3A and 3B (in a much-abbreviatedhistory window). The older version of the file consists of dataABCDEFGHIJ. The new version of the file consists of data ABCZZDEFGHIJ(the changes being the insertion of additional instructions/code/data“ZZ”). Initially, the entire older version of the file is loaded intothe history window. As characters from the new file are processed, theyare added to the window to supplement the compression dictionary. Oncethe window is filled to its capacity, each character added to the windowfrom the new file displaces a character from the old file out of thewindow.

An alternative arrangement is shown in FIGS. 4A and 4B. Again, the olderversion of the file (ABCDEFGHIJ) is preloaded into the window. Ascharacters from the new file are processed, they are added to thewindow. Once the window is filled to capacity, the new data slidesthrough the window, with each new character displacing anearlier-processed character. The older version of the file stays inplace.

If the history window is not large enough to contain the entire olderversion of the file, the beginning portion is desirably loaded in thewindow to the exclusion of the ending portion. (Statistically, itappears that correlation between different versions of the same file isgreatest at the beginning, so allocating the history window to thebeginning of the file optimizes compression.)

The foregoing assumes prior knowledge of the exact contents of a file onthe user's computer 20A. However, as suggested earlier, sometimes a fileis modified slightly when it is installed on the user's computer. Insuch cases, the file on the vendor's computer 20B is different than thefile actually resident on the user's computer 20A.

One reason the files may be different is due to binding. Binding is theprocess by which references external to the file are resolved prior toloading the file for execution. In the installation context, binding isthe process of determining the import addresses of other binariesexisting on the user's machine, and storing these address in a specialarea of the file to facilitate faster execution. For example, executablefile ABC.EXE may call functions contained in library USER32.DLL. To findthese functions, a string search must normally be performed on the fileUSER32.DLL installed on the user's computer in order to determine theappropriate file offset. Rather than undertaking this process each timefile ABC.EXE is executed, the process is performed once—when ABC.EXE isfirst installed. The applicable offsets are then stored in a tablewithin file ABC.EXE, making this data available for quick reference anytime the file is executed.

Another reason the files may be different is due to lock prefixinstruction smashing. Executable files are commonly written to run onseveral different hardware platforms. Instructions specific to oneplatform may be ignored when the file is run on a different platform.For example, if an executable program is written for bothsingle-processor and multi-processor platforms, the code will likelyinclude “lock-prefix” instructions that synchronize memory accesses whenthe file is executed on a multi-processor platform. Such instructions,however, are not needed if the code is run on a single-processorplatform, and only serve to slow execution.

Due to the performance penalty such superfluous instructions entail,they are commonly “smashed” when the file is installed on asingle-processor computer (i.e. replaced by no-operationinstructions—NOPs). Doing so speeds execution. However, this again meansthat the file as installed on the user's computer may not identicallymatch the file as distributed by the software vendor.

Yet another reason a user's files may be different from the vendor's isrebasing. Rebasing is a consequence of the fact that some programfiles—typically dynamic link libraries—have preferred addresses at whichthey are expected to be installed in order to make best use of memory.Data inside the file presupposes the file will be installed at thepreferred location. If an earlier program has already been loaded at thefile's expected address, the file must be loaded elsewhere in memory andall its internal references that depend on a specific load address mustbe adjusted accordingly. To avoid the performance penalty of performingthis relocation in memory each time the file is loaded, the file can berebased at installation time to an address range that is not used by anyother file on the user's computer. When the file is rebased in this way,the internal references are adjusted as necessary so that subsequentloading will not require relocation.

Before the file on the user's computer is patched (whether by thetechniques described above, or by prior art techniques), it is desirableto copy the file and “normalize” the copy to a predictable state. Sodoing assures that the file on the user's computer can be replicated onthe vendor's computer, so that appropriate patching instructions can begenerated.

Normalizing is essentially a process of removing any differences thatwould be created as a result of typical installation modifications.Binding, lock prefix removal, and rebasing are some of several suchdifferences that can be normalized.

Referring to FIG. 6, a first step in normalizing the file ABC.EXE on theuser's computer 20A is to remove any binding-specific information storedin the file. The addresses can be zeroed-out, or changed to any known orpredictable or computable value.

A second step is to normalize the smashed “lock prefix” instructions.Since not all “NOP” instructions in the user's file are necessarilysmashed lock prefix instructions, NOPs are not all converted to lockprefix instructions. Instead, all lock prefix instructions in the codeare uniformly converted to NOPs. (In a single-processor installation,some of the lock prefixes may not have all been smashed. In amulti-processor installation, none of the lock prefixes were earliersmashed.) While this process does not restore the file to itspre-installation form, it converts it to a known form—which is the moreimportant goal.

(Actually, during the build process of an executable file, most linkersautomatically create a lock prefix address table that is stored withinthe executable file. This table is used during installation of the fileto determine which instruction locations should be smashed on a singleprocessor computer. The same table can be used in normalizing, allowingthe NOPs formed by smashed lock prefix instructions to be identified andrestored to their pre-installation form. Again, the aim is simply toconvert the file to a known form; the precise form is not critical.)

A third step is to change the rebasing. One option is simply to zero allinternal file references in the old file, or change them to any otherpredictable or computable value. In the preferred embodiment, however,the user's old file is normalized in anticipation of the base addressemployed in the new file. In particular, the old file on the user'scomputer is not normalized until the update data is received from thevendor computer. Within the update data (e.g. in a header) is a fieldspecifying the base address used in the new version of the software. Ifthis base address does not match the base address in the user's oldfile, the normalization process steps through the old file, offsettingeach address by the difference between the old file's base address andthe new file's base address. In this manner, not only is the user's filebrought into a known state, but it is brought into a state that moreclosely corresponding to the new file, reducing the amount of updatedata that must be transferred.

Again, the results of such normalizations are not necessarily to restorethe file to the state it was in when originally received from thevendor, but to transform a copy of the user's installed file into a filewhose characteristics are reliably known. A counterpart such file, onthe vendor's machine, can then be used as a basis for determiningpatching instructions.

FIG. 7 illustrates the process. On the vendor's computer, the oldversion of the file is loaded into RAM memory. There it is normalized,as necessary, in accordance with FIG. 6. The normalized file on thevendor's computer is then compared with the new version of the file togenerate a patch file. (This “comparing” can be of the type describedabove, involving LZ compression wherein the history buffer is preloadedwith the normalized old file, or it can be done by any other technique.)

The patch file is next transferred to the user's computer. There, theold version of the file is copied from the user's hard disk into RAMmemory and normalized, in accordance with FIG. 6. The patch file is thenprocessed to generate—on the user's computer—a copy of the new file.Once the new file has been generated, it can be installed, if necessary.(The installation process may entail various steps in addition to thebinding, smashing, etc., operations reviewed above. For example, datafrom the new file may be entered into registry files maintained by theoperating system. For other files, no “installation” process is needed;they are stored on the computer directly as output from the patchprocessing.)

The normalizing operation can be invoked by instructions stored on theuser's computer, in which case the patch file has no additional overheadassociated with installation-specific file variations. Alternatively,the normalizing steps to be performed on the file can be specified in apreamble to the patch file received from the vendor. In the latter case,normalization operations specifically tailored to the file being updatedcan be performed.

From the foregoing, it will be recognized that the preferred embodimentprovides much smaller patch files than has been possible with prior arttechniques. Smaller patch files mean faster download times for on-linedelivery mechanisms, and reduced storage requirements for updatediskettes and the like.

The preferred embodiment also eliminates the two-step process at boththe vendor and user computers. Instead of (1) comparing files on thevendor computer to generate patching instructions, and then (2)compressing the patching instructions in a separate operation, thedetailed embodiment produces a compressed patch file in a singleoperation. Likewise on the user's computer, instead of (1) decompressinga patch file to obtain patching instructions, and then (2) performingthe patching instructions in a separate operation, a single processresults in generation of the updated file.

It will also be recognized that the above-described normalizing processallows a single patch file to be distributed for use on plural differentcomputers, even though the file to be updated on each computer isslightly different, due to installation modifications. The creation ofmulti-version update files (or multiple update files) to try and copewith multiple forms the file may take after installation, is thusobviated.

Having described and illustrated the principles of our invention withreference to an illustrated embodiment, it will be recognized that theembodiment can be modified in arrangement and detail without departingfrom such principles.

For example, while the invention has been illustrated with reference tosoftware-implemented compression and decompression processes, inalternative embodiments these, and other functions, can be implementedin dedicated hardware.

Similarly, while the invention has been illustrated with reference to aprocess in which the compressor/decompressor are pre-initialized inaccordance with an older version of the same file, in alternativeembodiments this need not be the case. Any data known to exist on theuser's computer—for which a copy is also available on the vendor'scomputer—can be used to pre-initialize the compressor/decompressor.

Many executable files, for example, have a high degree of redundancybetween each other due to the limited vocabulary of computerinstructions. Thus, a vendor who wishes to distribute a brand newapplication program, having no counterpart code already installed onusers' computers, can nonetheless gain substantial compressionefficiencies by compressing the program using a compressorpre-initialized with, e.g., a file known to be present on the user'scomputer. For example, if the application has been written for theWindows NT operating system, the vendor knows that the user's computerwill include a large group of known operating system files (e.g.WIN386.EXE, USER.EXE, VBRUN300.DLL, OLE2.DLL, WINFILE.EXE, WINHLP32.EXE,WIN.COM, etc.) in directories \WINDOWS or \WINNT, and \WINDOWS\SYSTEM.Moreover, the operating system software includes a large number ofapplication-like programs, such as Solitaire (SOL.EXE), Write(WRITE.EXE), etc. Depending on the type of code the vendor wishes todistribute, different operating system files can be used topre-initialize the compressor (and decompressor) to optimizecompression.

Naturally, the precise contents of a user's operating system filesdepend on the particular version and “build” of the operating systemthat is installed on the user's computer. Accordingly, care must betaken when presuming knowledge about files already available on theuser's computer. However, even though operating system files change fromone version to the next, much of the code is consistent throughout allversions of an operating system. Such known-stable segments ofcode—often excerpted from larger files—can be used to pre-initialize thecompressor/decompressor.

Particularly in contexts where the user's computer has no older versionof the same file being installed, it can be desirable to pre-initializethe compressor/decompressor in accordance with plural files (or fileexcerpts) from the operating system, rather than just one, reasoningthat the larger the source of pre-initialization data, the smaller theresulting patch file. (“Patch file” may suggest that an older version ofthe file is present and is being updated, but as used herein it alsorefers to a file that generates a brand new file.)

Generally speaking, if processing a *.EXE file, it is desirable topre-initialize the compressor/decompressor in accordance with one ormore *.EXE files. Similarly, if processing a *.HLP file, other *.HLPfiles are good choices for pre-initialization. Ditto *.DLL files.

While it has sometimes been suggested to preload the dictionary with adedicated vocabulary of expected high-frequency character strings (e.g.U.S. Pat. No. 5,652,878, and EP 462,363), the data used topre-initialize the compressor/decompressor in the illustrativeembodiment is different. Such data is not provided on the computerssolely as a compression expedient or aid. Rather, such data is presentbecause it is part of an operating system or application program, etc.Its use in this compression context is incidental and secondary to suchprimary use.

While the invention has been described as employing stand-alonecompression and decompression processes, such functionality can beintegrated into a more comprehensive set of programs, such as anoperating system update utility, or a web-based software installationaplet. It can also be desirable to provide the component parts of thedescribed functionality as operating system services, available througha family of file patching APIs (application programming interfaces).

While the invention has been described in the context of updating asingle file, it will be obvious to those skilled in the art canadvantageously be applied to updating a group of files, such as may beassociated with an application program or operating system.

Although the disclosure has focused on core processes, such asgenerating the update data and generating the updated file using same,it will be recognized that numerous known ancillary processes can beused in conjunction therewith. For example, the raw update data can beassembled into a self-extracting patch file. Execution of such a file onthe user's computer can: specify the file to be updated, load that filefrom the user's hard disk into memory, normalize the file preparatory toupdating, implement a software decompressor, pre-initialize thedecompressor in accordance with existing data on the user's computer;apply the update data to the decompressor, and take the resulting filedata and store it on the user's disk, or initiate any appropriateinstallation procedure.

While the illustrated LZ77 embodiment has been described as employing ahistory window of fixed size, those skilled in the art will recognizethat the same principles can likewise be applied to systems in which thehistory window grows.

It will be recognized that the old version of the file may have beeninstalled—sometime earlier—from a distribution media (internet ordiskette) by which it was delivered in compressed form. The old versionof the file may have thus been decompressed by a decompression process.In that process, data comprising the old version of the file wassuccessively added to the history window. In the weeks or monthsfollowing this original installation, that decompression code would havebeen terminated, the memory cleared and applied to other uses, and thefile used for its intended purposes. When the user desires to update thefile, the old version is restored to a history window, a curious déjàvu.

While the invention has been illustrated in the context of providing anewer version of software to a user's computer, there are situations inwhich it is sometimes necessary to regress and replace a newer versionwith an older version. The same process can naturally be used, bypre-initializing the compressor/decompressor in accordance with newerversion of the software, compressing the older version, etc.

Similarly, while the invention has been described in the context ofpatching “files,” the technology is not so limited. Patching canlikewise be applied to any stream of data, such a sequence of networkpackets, a sequence of key strokes, etc.

The above-described file normalizing processes are not limited to use inthe particular embodiment described above. The same techniques can beapplied in other, e.g. prior art, software-updating techniques to assurethat the file to which the patching instructions are applied is of knowncontent. Thus, it should be understood that aspects of theabove-described technology can be used independently, all together, orin various sub-combinations—as best fits the particular circumstances.

In view of the many possible embodiments to which the principles of ourinvention may be applied, it should be recognized that the detailedembodiments are illustrative only and should not be taken as limitingthe scope of our invention. Rather, we claim as our invention all suchembodiments as may come within the scope and spirit of the followingclaims and equivalents thereto.

We claim:
 1. A method of providing a new file on a computer, comprising:receiving update data at the computer; pre-initializing a decompressorin the computer in accordance with at least a portion of a referencefile available on the computer, the reference file being available onthe computer for a purpose other than serving as a decompression aid;and decompressing the update data with the decompressor to produceoutput data, wherein the output data is the new file.
 2. The method ofclaim 1 in which the pre-initializing includes copying said portion ofthe reference file into a history window associated with saiddecompressor.
 3. The method of claim 1 in which the pre-initializingincludes performing a compression operation on said portion of thereference file.
 4. The method of claim 1 which includes pre-processingthe reference file to normalize same.